Heat exchange devices are used on a large scale in many branches of industry, e.g. in the petroleum industry for cooling products obtained from hydrocrackers and reactors for partial oxidation of (hydro)carbon-containing fuels such as oil and coal and the like.
When used for cooling purposes, the hot gases are passed through tubes which are cooled with a cooling medium on the outside. The walls of the tubes acquire a high temperature owing to transfer of heat from the hot gases to the tube metal which heat is further transmitted to the cooling medium. Advantageously, for reasons of space saving, helically coiled tubes are applied.
Dependent on the field of application, technical problems of different nature are met.
For example, the cooling of hot gases obtained from the gasification of (hydro)carbon-containing fuel, in which the presence of small solid particles is unavoidable, involves serious heat transfer problems and erosion/corrosion problems.
Hot synthesis gas produced by partial oxidation of (hydro)carbon-containing fuel is generally cooled in a heat exchanger located next to the gasifier thereby producing high pressure steam. A critical area is the gas inlet of the heat exchanger where the hot synthesis gas enters the heat exchange area. The wall thickness of the inlet area is to be minimized but should be thick enough to ensure mechanical integrity based on pressure and thermal loads. The gas velocity at the inlet area should be sufficiently high to prevent fouling but on the other hand low enough to ensure sufficiently low gas side heat transfer coefficients. In particular, obtaining an optimum between fouling and velocity is desirable.
U.S. Pat. No. 4,029,054 and U.S. Pat. No. 3,610,329 disclose apparatus for cooling of hot gas wherein the upstream part of the gas tubes is positioned in refractory material. The upstream part of each gas tube is separately cooled by water supplied with a dedicated supply conduit. The used cooling water is discharged to the main cooling compartment via an annulus between the refractory material and the gas tube.
FR-A-2284851 describes an apparatus for cooling of hot gas wherein the upstream part of the gas tubes are positioned in the main cooling compartment. The gas tubes are not surrounded by an annular space. The gas inlet plate is spaced away from the wall, which wall has the same convex shape thereby defining the cooling compartment wherefrom the used cooling medium is discharged via separate conduits.
A disadvantage of the cited prior art is the complexity of the apparatus due to the existence of multiple separate supply or discharge conduits.
EP-A-774103 describes an apparatus for cooling of hot gas wherein the inlet section is cooled by passing fresh cooling medium, i.e. water, along the exterior of the upstream end of the heat exchanger tubes. The flow of water is counter-current to the flow of hot gas within the tubes.
WO-A-2005116560 describes an apparatus for cooling of hot gas wherein the inlet section is cooled by passing fresh cooling medium, i.e. water, along the exterior of the upstream end of the heat exchanger tubes. The flow of water is co-current to the flow of hot gas within the tubes.
U.S. Pat. No. 5,671,807 discloses an apparatus for cooling of hot gas wherein the inlet section is cooled by passing fresh cooling medium, i.e. water, along the exterior of the upstream end of the heat exchanger tubes. The flow of water is co-current to the flow of hot gas within the tubes.
WO-A-2005015105 describes an apparatus wherein the inlet section is cooled by using fresh liquid cooling medium and a defined part of the liquid cooling medium is present in the main cooling compartment. In this prior art apparatus, although the steam production is high, there is room for improvement in view of the high heat capacity of the hot gas to be cooled. Furthermore separate conduits for supply and/or discharge of the cooling medium for each gas tube make the design complicated, the positioning of the tubes is inconvenient for replacement in case of failure, and the proposed design does not secure the operation under high pressure, especially above 9 MPa.